Plant-based essential oils are widely used in perfumery, food and flavor components, preservatives, household and laundry deodorizing, and medicinal treatments such as aromatherapy, topical pain relief, arthritis, and acne. An essential oil is a liquid containing volatile aroma compounds obtained from plants. It is “essential” as it contains the “essence of” the plant’s olfactory attributes. This property renders them “essential” in the composition of many fragrance additives used in cosmetics formulations, aromatherapy, massage oils, and medicinal agents.

Essential oils can penetrate skin and enhance topical delivery of active agents from topical formulations via a variety of mechanisms, which include disintegration of intercellular lipid structure in stratum corneum, interaction with intercellular proteins, and increasing the distribution of an active agent through the cellular membrane barrier. After skin penetration, essential oils are rapidly metabolized and excreted, suggesting their use as safe skin permeation enhancers.1 However, an unintended enhancement of an active agent into skin can also cause efficacy and safety concerns.

Meditation, massage, and medicine can all be practiced via aromatherapy. The benefits of aromatherapy are well documented, ranging from the treatment of mild sleep disturbances2 as an adjuvant treatment in cancer care,3 and massage therapy.4 The therapeutic utilization of essential oils, coupled with their skin penetration and inhalation exposure, can pose both enhanced benefits or significant toxicological concern, especially in terms of skin sensitization, irritation, allergic reactions, and contact dermatitis.5 Relative to allergic reactions, a large number of essential oils are used in cosmetics as aroma ingredients. In a literature study of 517 cosmetics formulations, 11 substances recognized as allergens were found in the essential oils used as fragrance components.6

An indiscriminate use of an essential oil or an aroma ingredient in a cosmetics formulation without the knowledge of the toxicology of their chemical constituents or biological effects is cause for concern. The knowledge of such information for cosmetics formulators, estheticians, and healthcare personnel can be highly beneficial for the consumer.7 This article shall present natural essential oils that are beneficial for skin and their application in topical body care applications and preservation of cosmetics formulations.

Massage Therapy for Holistic Well-Being

Essential oils for massage therapy and topical pain management are well-documented from antiquity: myrrh being the legendary example. In recent years, massage therapy has emerged as one of the most important complementary and alternative therapies for the management of a variety of ailments.

Massage therapy is an art and a science. The safe, non-pharmacological method of aromatherapy massage can be readily integrated into clinical practice. Well-known essential oils, such as rosemary, geranium, lavender, eucalyptus, and chamomile have been safely used. However, training and experience of aromatherapy and knowledge of the properties of essential oils used by massage personnel is critical to achieving optimal results.15

Massage and reflexology are simple and effective treatments that can be used to help manage pain and fatigue in patients with rheumatoid arthritis.16 A combination of aromatherapy massage and inhalation aromatherapy has been clinically proven to reduce burn patients’ anxiety and pain.17

In a clinical trial, 90 patients with osteoarthritis of the knee were studied in three groups: 1) treatment: massage with lavender oil; 2) placebo: massage with almond oil; and 3) control: without massage. Aromatherapy massage with lavender essential oil was found most effective in relieving pain in these patients.18

In another clinical trial, comparing the effectiveness of aromatherapy and acupressure massage therapies on the sleep quality of women, all experimental groups (blended essential oil, lavender oil, and acupressure massage) showed significant improvements in sleep quality. However, a significantly greater improvement in sleep quality was observed in the blended essential oil groups compared with the lavender oil group. This suggests use of a blend of essential oils to be better than a single entity.19

In a study to determine the effect of aromatherapy massage on quality of sleep and physiological parameters in intensive care patients, aromatherapy massage enhanced the sleep quality of patients and resulted in positive changes to their physiological parameters.20

Abdominal massage with essential oils has been found to be an effective complementary method to relieve menstrual pain (dysmenorrhea).21

The experience and knowledge of the massage therapist and selection of the right composition of massage oil are critical in the success of this ancient treatment method for providing relief and relaxation to the consumer.

Dermatological Safety of Massage Oils

Skin occupies a rather large surface area (~1.5 to 2.0 square meters). Exposure to any treatment with the massage oil can cause consumers perceived discomfort from erythema, irritation, and dermatitis.

Blended fragrances and natural essential oils have been used in perfumery and cosmetics. While many essential oils are now known to cause skin sensitization and dermatitis, the testing of fragrance oils that may contain such essential oils, for example Santalum album, Cananga odorata, Jasminum species, Mentha piperita, Melaleuca alternifolia, tea tree oil, and Lavandula angustifolia, may not reveal this potential safety concern (unless such essential oils are tested themselves).22

Even certain essential oils approved by the FDA as OTC external analgesics (for example, camphor, menthol, methyl salicylate, and turpentine oil), are classified as counter-irritants by the FDA monograph on External Analgesics Drug Products for Over the Counter Human Use. A number of essential oils, used as fragrances, are labeled by their INCI names on cosmetic products, which could be confusing to consumers in terms of ascertaining their dermal safety.23 To illustrate this further, contact dermatitis has been reported with a number of commonly used massage essential oils, including turmeric,24 eucalyptus and tea tree oils,25 lavender oil,26 citral (lemon oil),27 ylang ylang,28 sandalwood,29 and jasmine absolute.29 INCI names of these oils on a product label are not reflective of their common identity, hence not readily recognized by consumers.

Among 80 essential oils tested, oils from laurel, turpentine, orange, tea tree, citronella, ylang ylang, sandalwood, clove, and costus root have all shown strong contact allergy.30 Additionally, co-reactivity with other essential oils, fragrance compositions, and other formulation components (which could enhance their skin penetration) is rather common.31 Since many of these essential oils may contain 50-200 individual chemical entities it is not always possible to pinpoint cause for such allergic responses.

In view of the aforementioned concerns, patch testing of individual components of essential oil blends and fragrances to ascertain their skin safety needs serious consideration before a product launch.31 A product recall or regulatory action based on consumer complaints is not a pleasant business matter.

Natural Oils for Massage Therapy

Massage with seed oils to alleviate pain has been practiced since ancient times. The clinical data on the efficacy of such treatments is recently of scientific interest. A clinical study found massage with topical sesame oil on limb trauma patients significantly reduced pain severity.32

In another clinical trial, infants were treated with olive oil massage for 10 days (three times for 15 minutes a day) and control group infants were massaged without olive oil. The neonatal weight gain in the infants with the oil massage was 21 grams daily in average, whereas the increase in infant massage without oil was 7 grams. The positive effect of infant massage with olive oil on weight gain in premature infants was recommended.33 However, in another study the use of topical oils on baby skin was shown to contribute to development of childhood atopic eczema.34

Natural oils are used throughout the world for general skin and hair care. However, there is a lack of scientific evidence to support this practice. In a recent study the effect of olive and sunflower seed oils on stratum corneum integrity and cohesion was studied. Topical application of olive oil for four weeks significantly reduced stratum corneum integrity and induced mild erythema. Sunflower seed oil preserved stratum corneum integrity with no erythema, and improved hydration. In contrast to sunflower seed oil, topical treatment with olive oil significantly damages the skin barrier, and therefore has the potential to promote atopic dermatitis.35

In another clinical trial comparing sunflower oil to an emollient on barrier development in healthy term newborns, both skin care regimes did not harm skin barrier function. The fatty acid content of seed oils seems to be a controlling factor for barrier function disorders (oleic acid being most disruptive).36

Coconut oil massage has been reported to reduce transepidermal water loss in neonates without effect on topical skin microbes.37 In a comparative study, coconut oil was found superior to olive oil in skin moisturization and antibacterial protection.38 Similarly, coconut oil was found superior to mineral oil in treating atopic dermatitis in a study of 117 patients.39

The intercellular lipids of stratum corneum help maintain the skin barrier function. In a study to evaluate the effect of topically applied paraffin, petrolatum, almond oil, and jojoba oil on the intracellular lipid profile of stratum corneum, the plant-derived oils significantly changed the intracellular lipids.36,40 Squalane, now available from plant-based technology, could be an alternative for petroleum-based oils (mineral oil, paraffin) for massage applications.

It is worth noting that the (saturated) fats and oils that are not good nutritionally are better suited for topical applications. Conversely, the (unsaturated) fats and oils that are better suited for nutritional purposes41 are not suitable for skin care applications. This divergence could be of significance in the selection of oil/fat in emulsion-based skin care lotion and cream formulations.

Formulation Strategy for Massage Oils

The formulation of safe and functional massage oils should focus on the following minimal attributes:

Pleasant aroma,

Skin safety,

Perceived consumer benefit,

Ease of application, and

Cost viability.

For this reason, the use of pure essential oils or certain seed oils must be avoided. The inclusion of a small quantity of an essential oil (for sensory benefits and formula esthetics) blended with a (mostly saturated) seed oil or hydrocarbon oil is prudent. This strategy can even reduce the amount of preservative for such formulations.38,42

Essential Oils as Preservatives

Many essential oils possess excellent antimicrobial and antifungal activity. Coupled with their insensitivity to varying pH ranges, their application as preservatives for cosmetics, foods and pharmaceuticals is receiving increasing attention. Consumer sensitivity due to reported allergic contact dermatitis of synthetics,43 and the development of resistant bacteria in cosmetics preserved with synthetic antibacterial agents is further driving this trend toward natural preservatives.44

It is worth noting that the use of synthetic preservatives at their recommended dose levels did not seem to cause any skin irritation in an analysis of 45,000 human subjects.45 While a large number of essential oils are known to possess antibacterial and antifungal activity, their safety, efficacy, and stability in formulated cosmetics as preservatives has been of limited scope. A number of such preservatives contain phenolic or polyunsaturated antimicrobial and antioxidant components, which renders them sensitive to discoloration due to air oxidation (especially in formulations above pH 8.0 and/or presence of oxidizing metals such as copper, iron, and nickel.

A few recent examples of essential oil-based preservatives in formulated products are noted here in anticipation of further commercial development of essential oils as cosmetics preservatives. In this regard, the olfactory and color attributes of certain essential oils continue to pose formulating challenges as preservatives. The essential oil of curcumin (Curcuma longa), for example, has shown potent antibacterial and antifungal activity.46 The yellow color and strong medicinal odor of turmeric oil prevents its use as a natural preservative in cosmetics. Ginger oil has been reported as a good preservative for fish products.47 The strong, spicy aroma of this oil, however, does not offer promise for its use as a cosmetic preservative.

Salva-de-marajó: Plants of Lippia sp. (origanum family) are well known for their aromatic constituents. Lippia origanoides is a very aromatic shrub distributed from North America to South America, with prominent occurrence in the Amazonian region of Brazil, the Guianas, Venezuela, and Colombia.48

A recent study on the essential oil of L. origanoides, which consisted mainly of oxygenated monoterpenes (38%) and carvacrol (26%), showed that it inhibited the growth of all the tested microorganisms. The Ames test indicated that this oil was non-mutagenic. In combination with polysorbate 80, the essential oil exerted preservative action on orange juice, as well as cosmetic and pharmaceutical compositions, especially in the case of aqueous-based formulations.49

West Indian Raspberry (Rubus rosifolius): This plant is a prickly shrub native to rainforests and forests of the Himalayas, East Asia, and eastern Australia. The extract of this plant was evaluated as a preservative at 0.2% (w/w) use level in two different base formulations (emulsion and gel). The microbial challenge test was performed with the standardized microorganisms. The results demonstrated the extract reduced the bacterial inoculate. However, it was not an effective preservative against fungi, thus requiring a complementary antifungal agent.50

Self-Preserving Cosmetics: An emerging trend of self-preserving and preservative-free cosmetics is on the horizon. This feat is achieved by using a combination of antioxidants, chelating agents, and bioactive essential oils.51 Phenethyl alcohol, an essential oil component of rose oil, in combination with caprylyl glycol and glyceryl caprylate, is a new preservative for emulsion formulations, especially those of droplet particle size in the range of 100-900nm.52 A design space model for preservative optimization, developed for synthetic preservatives, may be applicable for natural ingredients-based cosmetic preservatives.53

The future of self-preserving and preservatives-free formulations is of limited practicality due to a plethora of reasons, including limited availability of natural preservatives with proven broad-spectrum efficacy at low (0.1-0.5%) use levels, the complexity of additives and ingredients in a formula, pH ranges, stability criteria, activity against mutations of resistant bacteria, and regulatory requirements of such formulations.

Summary

The formulation of essential oil-based massage oils requires a prudent selection of essential oils and other emollient ingredients for their consumer acceptance, skin safety, and sensorial attributes. The application of essential oils for preservation of cosmetics replacing synthetics is still in its developmental stages.

The use of seed oils for massage requires a careful selection of such oils. Oleic acid, among all other fatty acid constituents of seed oils, has been shown to penetrate skin the most.54 This may explain why olive oil causes dermatitis on topical application. The oils that are high in oleic content (C18-1) need discretion for massage applications.

The technologies for preservative-free cosmetics are envisioned to be of limited applicability due to the variety of ingredients used in such formulations. The mutations of bacteria resistant to synthetic and other preservatives in cosmetics formulations shall pose additional challenges for preservatives-free cosmetics research.

About the author: Shyam Gupta is an international consultant in innovative topical and skin care formulations based on new ingredients and delivery systems with over 100 patents, patent applications, cosmetics publications, and book chapters. He specializes in consumer-desirable, nature-based ingredients with incomparable efficacy and performance attributes. For more information: 602-996-9700, E-mail: shyam@biodermresearch.com, Website: www.biodermresearch.com.